1. Field of the Invention
The present invention relates to broadband signal switching apparatus of the type which comprises cross point matrix constructed in field effect transistor (FET) technology whose switch elements are each formed with a switching transistor charged with a through-connect or, respectively, inhibit signal at its control electrode and having its main electrode connected to the appertaining matrix output line.
2. Description of the Prior Art
Recent developments in telecommunications technology have led to integrated services communications transmission and switching systems for narrow band and broadband communications services which provide light waveguides as transmission media in the region of the subscriber lines by way of which both the narrow band communications services such as, in particular 64 bit/s digital telephony, and broadband communications services such as, in particular, 140 Mbit/s picture telephony, are conducted, whereby narrow band signal switching equipment and broadband signal switching equipment are, however, provided side-by-side in the switching stations (preferably comprising shared control devices such as in the German patent No. 24 21 002).
It is known, in conjunction with broadband signal time-division multiplex switching device whose crosspoints are respectively utilized in time-division multiplex for a plurality of connections, to connect respectively two lines with the assistance of a gate which is switched on and off by a cross-point-associated memory cell constructed as a bistable D flip-flop, whereby this cross point-associated memory cell whose clock input is supplied with a corresponding clock signal is selected in only one coordinate direction, namely at its D input (Pfannschmidt: "Arbeitsgeschwindigkeitsgrenzen von Koppelnetzwerken fur Breitband-Digitalsignale", dissertation, Braunschweig 1978, FIGS. 6.7 and 6.4). In view of the time-division multiplex factor of about 4-8 obtainable given a bit rate of 140 Mbit/s and of the involved circuit technology thereby required, however, pure space switching equipment are currently preferred for switching broadband signals, the connections through-connected via the individual cross points being separated only spatially from one another therein.
A pure broadband signal space switching arrangement can be constructed as a cross point matrix in complementary metal-oxide-semiconductor (CMOS) technology provided with input amplifiers and output amplifiers in whose cross points the switching elements are respectively controlled by a decoder-controlled, cross point-associated holding memory cell, whereby the switching elements are respectively fashioned as CMOS transfer gates (CMOS transmission gate as in ISS'84 Conference Papers 23Cl, FIG. 9); the cross point-associated holding memory cells of a pure space switching matrix can be selected in two coordinates proceeding from a row decoder and from a column decoder, being respectively selected via a row-associated or, respectively, column-associated selection line (Pfannschmidt, OP.CIT, FIG. 6.4).
It is also known in general form (from Electronics, Dec. 15, 1983, pp. 88-89) to provide digital cross points in the form of tristate inverters in a broadband signal cross point matrix, the concrete realization of these, however, still remaining unanswered.